Those first two conditions parallel this season. Jason Kelce's torn medial collateral ligament and anterior cruciate ligament last week sidelined him for the remainder of the schedule, and the Eagles are giving the job to Dallas Reynolds, a three-year practice-squad player whose first snap came last week after Kelce's injury. He will start his first game on Sunday against the Arizona Cardinals.
The team also signed veteran Steve Vallos for insurance. Suddenly, a position central to the rest of the offense entered the spotlight because there is so much responsibility placed on the Eagles' starting center and there is so little known about Reynolds.
"It's like the changing sands of Cape Cod over there," Eagles coach Andy Reid said of playing center.
That's why Reid looks for three characteristics in his centers: They must be smart, must be able to quickly make adjustments, and must possess athletic ability. Those are common in most franchises, and illustrate why centers are difficult to find and imperative to develop.
The Eagles consider their center an extension of the quarterback and head coach, which is why so much time is invested in measuring football intelligence. General manager Howie Roseman said that when Eagles scouts meet with prospective centers during the predraft process, they use the meetings to assess intelligence.
This is in addition to the skills and athleticism ordinarily sought in a center. Because the position's requirements have as much to do with intelligence as size, college guards - and even tackles - are sometimes turned into centers upon reaching the NFL. Reynolds was a tackle until his final year at Brigham Young. Vallos was a tackle at Wake Forest. They competed in training camp with Mike Gibson, who was a tackle at California, and Julian Vandervelde, a guard at Iowa. Kelce had arrived at Cincinnati as a linebacker.
"It's a position where guys are sometimes forced into it because they're so smart, but they're not as athletic," Vallos said. "Some of these guys that get drafted in the first round, you don't usually see centers because they're not these freak athletes. But they're smart and can put guys in the right places."
The Eagles and other NFL teams can uncover an eventual starter late in the draft or among the undrafted free agents because centers are sometimes developed more than selected. Fraley, Jackson, and Reynolds were undrafted. Kelce was a sixth-round pick.
The earliest the Eagles have drafted a college center in the Reid era was the fourth round in 2002 (Scott Peters). Of the NFL's 32 starting centers, eight were undrafted, and five were drafted in the last two rounds. Six were first-round picks and seven were second-round picks.
This is also because teams tend to build their offensive lines from the outside in. Tackles are the highest drafted and earn the most money. Then come guards and centers. In the last 10 drafts, 33 first-round picks were spent on tackles, nine on guards, and seven on centers.
"It's hard to find starting tackles, guys who are big and athletic and mobile and facing different guys than inside guys," Roseman said. "But that doesn't diminish the importance of your interior offensive linemen."
Quarterback of the line
Reynolds spent three seasons on the Eagles' practice squad, an experience akin to graduate school for playing center. He called it an "eye-opener" when he realized the responsibilities required of the position. It's why Fraley and Jackson, in separate telephone interviews this week, called the center "the quarterback of the offensive line."
"He's the guy who gets all five [linemen], including the tight end, the running back and the fullback, going in the right direction," said Jackson, who is now a free agent.
The center keeps his head up at the line to scan the defense. It's his responsibility to identify the "Mike" (middle linebacker), process what he sees, and then make protection calls.
Fraley said centers must be confident in these calls, like quarterbacks. If the center is indecisive, the play could break down. Jackson said the center must also be a leader because if someone else on the line struggles, the burden is on the center.
Eagles guard Evan Mathis said it has been "business as usual" for the offensive line with Reynolds replacing Kelce, and Reynolds is expected to fill all of Kelce's responsibilities. There was much excitement during the offseason about Kelce's improvement making calls and the greater role he'd have at the line of scrimmage. The same will be expected of Reynolds.
"He's a smart kid," Reid said. "He's able to handle all of that."
From reserve to starter
Fraley's first snap was a fumble. He survived to center four offensive lines that reached the NFC championship game, but he said tevery new center endures nerves before the first start.
"There's always going to be growing pains when people are first getting in there and playing," said Fraley, who is now an assistant coach at the University of San Diego. "But I learned from the guys in front of me. You learn from their mistakes. You learn what works, what doesn't. You're always practicing to be ready to fill in their shoes. Doesn't matter if you're on the practice squad, the backup, or the third backup."
Fraley added that Reynolds can lean on the other offensive linemen and offensive line coach Howard Mudd, and that Reynolds' experience in Philadelphia will help. It aided Fraley and benefited Jackson, although nothing can simulate the first start.
"It's really difficult because you got to get the trust of the guys around you," Jackson said. "You also have to have that relationship with your quarterback."
The Eagles scored 17 points last week after Reynolds entered the game, and Michael Vick met with Reynolds during the week. But Reynolds also said that the suddenness of his participation in last week's game allowed him to play unburdened. This week, he's taken the first-team repetitions during practice and conducted media interviews after practice. That can fill a newcomer's head, which Fraley said could be a problem.
"The biggest thing for any young guy or any player - I don't care if you have 10 years in the league - is to go out and play and not think about it," Fraley said. "Don't let it overwhelm you. It's just playing ball."
Fraley and Jackson will be rooting for him. They were once in the same position - an undrafted player who had been overlooked and underappreciated, taking a starting job with no experience. It worked for both of them, and they're hoping it works for Reynolds.
"I was happy for him that he even made the team, and now he gets a chance to show what he's got early in the year against a pretty good Cardinals defense, away," Jackson said. "It's going to test him a little bit. And hopefully he comes out on top."
Contact Zach Berman at firstname.lastname@example.org. Follow on Twitter @ZBerm.